In a photolithography process for producing a semiconductor device, a liquid crystal display, or the like, a pattern is formed by irradiating a semiconductor wafer or an original plate for liquid crystal, to which a resist film has been applied, with light through a photomask. If foreign matters adhere to the photomask to be used at this time, the foreign matters absorb the light or bend the light, so that there is a problem that the transferred pattern is deformed or the edge becomes coarse, and further the base becomes black and dirty, and the dimension, the quality, the appearance, or the like is impaired.
For this reason, the photolithography process is usually performed in a clean room, however, it is still difficult to keep the photomask clean, so that a foreign-matter guard called a pellicle is attached to the photomask.
A pellicle is usually constituted of a pellicle frame in a frame shape, a pellicle film stretched on an upper end face of the pellicle frame, an airtight gasket formed on the lower end face of the pellicle frame, and the like. The pellicle film is constituted of a material exhibiting high transmittance for exposure light, and a pressure-sensitive adhesive or the like is used for the airtight gasket.
If such a pellicle is attached to a photomask, foreign matters do not adhere directly to the photomask but adhere to the pellicle. In photolithography, if the exposure light focuses on a pattern of the photomask, the foreign matters on the pellicle becomes irrelevant to the transfer, and a problem such as deformation of pattern can be suppressed.
By the way, in such a photolithography technique, the shortening of wavelength of an exposure light source is under way as a means for increasing the resolution. To date, the exposing light source has shifted from a g-line (436 nm) or i-line (365 nm) by a mercury lamp to a KrF excimer laser (248 nm) or ArF excimer laser (193 nm), and further, the use of extreme ultra violet (EUV) light having a main wavelength of 13.5 nm is also studied.
On the other hand, as the wavelength of the exposure light becomes shorter, the irradiation energy also becomes higher, and as a result, there is a problem that foreign matters called haze are easily generated on a photomask. It is considered that such a haze is caused by foreign matters generated due to a reaction of NH3 gas present in the exposure environment, SOx gas, organic components, or the like, which is generated from a pellicle constituent member, by irradiation energy of exposure light.
Therefore, in JP-A 2009-169380 (Patent Document 1), it has been proposed that by coating a pellicle frame with an inorganic compound containing carbon, the amount of the gas released from the pellicle frame is suppressed, and the generation of haze is suppressed.
In addition, in JP-A 2013-7762 (Patent Document 2), or in JP-A 2013-20235 (Patent Document 3), a method in which by obtaining a pellicle frame by forming an anodic oxide film on a surface of an aluminum material by performing an anodic oxidation treatment using an alkaline aqueous solution containing citric acid or tartaric acid, the content of an inorganic acid such as sulfuric acid or phosphoric acid is reduced and the generation of haze is prevented has been proposed.
However, even by the techniques as described above, the generation of haze cannot be still completely prevented.